Patients enrolled in the study will undergo image-guided, volumetric intensity-modulated arc radiotherapy (IGRT-VMAT) with state-of-the-art treatment-planning and quality assurance procedures with emphasis on normal tissue sparing and delivery accuracy via the use of devices that ensure stability and beam location reproducibility. A rectal balloon with air filling will be used for prostate target immobilization and anatomical reproducibility, while a urethral catheter loaded with beacon transponders will be used to ensure set-up reproducibility and online target tracking. Previously untreated patients with prostate cancer will be treated with 45 Gy in five fractions of 9 Gy over 5 consecutive days.